1. Field of the Invention
The present invention relates to an azimuth angle setting device of a surveying instrument, and more particularly to a surveying instrument having a collimating telescope and an angle reader which produces an electrical signal corresponding at least to a horizontal angle.
2. Related Background Art
In the surveying instrument such as a transit having a collimating telescope having a collimating line set to cross a vertical axis and a horizontal angle readout scale, the magnetic north is examined by a compass and a scale is set to 0.degree. while the collimating telescope is oriented to the magnetic north, and then the collimating telescope is oriented to a collimating point to be measured so that an azimuth angle is detected with reference to the magnetic north. In this method, however, a high precision compass is required, and if there is a ferromagnetic material in a vicinity of the surveying instrument, an error is included in the azimuth angle. In a method for determining the azimuth angle without using the compass, a coordinate of the surveying instrument is determined by a back intersection method based on two or more known positions, one of the known collimating points is collimated, an azimuth angle is calculated by a desk-top calculator and the resulting angle is entered into the surveying instrument. This method results in errors in calculation and decrease of work efficiency.